@Ana21088 Yes, the service fee has nothing to do with the host- it's Airbnb's charge. Perhaps the host has some other discount settings (weekly, monthly, etc) that are conflicting with this one and causing the problem. But it's the host's problem to work out with Airbnb, there's nothing that you as a guest can do about it. The answer the host says she was given sounds wrong-she should contact them again in the hopes she'll get a better rep who can help correct the special offer function.
There are also a lot of glitchy issues with the platform lately, not sure why, but it may have to do with them having to let go 1900 employees a couple weeks ago, so there may not be the manpower to correct platform issues in a timely fashion.